This invention relates to a circuit arrangement for operating a discharge lamp provided with a DC-AC converter and with a starter circuit for starting the DC-AC converter, in which starter circuit means are present for generating a starting pulse through charging of capacitive means.
A circuit arrangement of the kind mentioned in the opening paragraph is known from U.S. Pat. No. 4,042,852. The known circuit arrangement is suitable for connection to an AC-voltage source of 50 to 60 Hz, the supply voltage being delivered to the DC-AC converter after full-wave rectification and through a buffer capacitor. As a result, the starter circuit for starting the DC-AC converter, and thus for charging the capacitive means, only serves to generate a starting pulse for starting the DC-AC converter after connection to the supply voltage.
In modern circuit arrangements, which also comprise means for controlling the luminous flux generated by the lamp, the DC-AC converter is supplied by means of a comparatively high DC voltage which is realised by means of a switch-mode power supply. Control of the luminous flux is realised then in that the operation of the DC-AC converter is periodically interrupted for short time periods. Under such circumstances it is necessary for the starter circuit to generate starting pulses in quick succession. It is usual for the periodic interruption to take place with a repetition frequency having a value situated in the range from approximately 100 Hz to approximately 100 kHz. The duration of the interruption may then lie between 100 Hz to approximately 100 kHz. The duration of the interruption may then lie between 0 and 1 times the period of the repetition frequency.